netfilter: ipt_CLUSTERIP: fix refcount leak in clusterip_tg_check()

The issue takes place in one error path of clusterip_tg_check(). When
memcmp() returns nonzero, the function simply returns the error code,
forgetting to decrease the reference count of a clusterip_config
object, which is bumped earlier by clusterip_config_find_get(). This
may incur reference count leak.

Fix this issue by decrementing the refcount of the object in specific
error path.

Fixes: 06aa151a ("netfilter: ipt_CLUSTERIP: check MAC address when duplicate config is set")
Signed-off-by: Xin Xiong <xiongx18@fudan.edu.cn>
Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/ipt_CLUSTERIP.c

@@ -520,8 +520,11 @@ static int clusterip_tg_check(const struct xt_tgchk_param *par)
 			if (IS_ERR(config))
 				return PTR_ERR(config);
 		}
-	} else if (memcmp(&config->clustermac, &cipinfo->clustermac, ETH_ALEN))
+	} else if (memcmp(&config->clustermac, &cipinfo->clustermac, ETH_ALEN)) {
+		clusterip_config_entry_put(config);
+		clusterip_config_put(config);
 		return -EINVAL;
+	}
 
 	ret = nf_ct_netns_get(par->net, par->family);
 	if (ret < 0) {